Industrial automation control systems comprise an industrial controller, which is a special purpose computer used for controlling industrial processes and manufacturing equipment on a real-time basis. Under the direction of a stored program, the industrial controller examines a set of inputs reflecting the status of the controlled process and changes a set of outputs controlling the industrial process. The inputs and outputs may be binary or analog. Typically, analog signals are converted to binary data for processing.
Industrial controllers differ from conventional computers in that their hardware configurations vary significantly from application to application reflecting their wide range of uses. This variability is accommodated by constructing the industrial controller on a modular basis having removable input and output (I/O) modules that may accommodate different numbers of input and output points depending on the process being controlled. The need to connect the I/O modules directly to or adjacent different pieces of machinery that may be spatially separated has led to the development of distributed I/O systems that take a variety of forms. In one example, a single discrete or “block” I/O module is located where desired. The block I/O module typically contains digital or analog I/O circuits or a combination of both, a built-in power supply, and a built-in network adapter for communicating with the industrial controller. In another example, the distributed I/O installation is modular in the sense that a single network adapter module is connected to the data network at a point remote from the industrial controller, and one or more I/O modules, as needed, are connected to the network adapter module for communication with the industrial controller through the single network adapter module.
In these modular distributed I/O products, the individual I/O modules communicate with the network adapter module by means, of a backplane. In some cases, the backplane is constructed in advance to have a finite number of slots each adapted to receive an I/O module, and the I/O modules (or a non-functional filler module) are plugged into the slots of the backplane. In others, the backplane has no predetermined structure and is built by interconnecting I/O modules to each other, either directly or using cables.
In either case, known modular products for distributed I/O applications are sometimes found to be sub-optimal for particular installations. When the distributed I/O system has a finite number of slots available to receive an I/O module, the number of slots can sometimes be insufficient. In the case where the backplane is constructed as and when the I/O modules are interconnected, the physical size of the I/O system can become undesirably large and can exceed the available mounting space on the machine being controlled and/or in an enclosure.
In some cases, cables have been used to extend a backplane from a first mounting location to a second mounting location, e.g., from a first fixed-length backplane to a second, or from a first enclosure to a second, to allow the various I/O modules to communicate with the industrial controller through a single network adapter. While this backplane extension technique is often effective, it does have numerous drawbacks including the relatively high cost of cables and the cable-to-backplane interface, the limited distance (about 1 meter), degradation of the electrical signals, wire congestion, possibilities for environmental contaminations at the cable-to-backplane connection. Also, in some cases, cables cannot be used due to moving machine parts or other undesirable environmental conditions.
In light of the foregoing issues and others, a need has been found for a wireless backplane extender for a distributed modular input/output system in an industrial automation control system.